In mobile phone positioning, there is a kind of positioning called base station positioning, that is, the mobile phone is located through the base station. The key here is how to calculate the distance from the mobile phone to the base station?
According to the distance formula S=V*T.
Since the speed of electromagnetic waves is the speed of light, if the propagation delay of the signal from the mobile phone to the base station can be calculated, the distance from the base station to the mobile phone can be calculated.
In this way, the problem of the mobile phone to the base station is transformed into the problem of how to calculate the transmission delay of the burst signal from the mobile phone to the base station!
The problem of transmission delay has been disassembled and disassembled in the synchronization of mobile phones and base stations and random access of mobile phones. Here we will analyze it again from the perspective of mobile phone positioning.
0. The mobile phone synchronizes with the base station through the synchronization channel of the base station
(1) Frequency synchronization: crystal oscillator frequency synchronization
(2) Time slot synchronization, the same period, but the absolute phase is not aligned, there is a delay t1.
(3) Frame synchronization: get the TDMA frame number
1. Random access process to obtain TA
(1) Through random access, the delay time TA=t1+t2 of the uplink and downlink is used to obtain the initial distance between the mobile phone and the base station.
(2) The base station tells the TA value to the mobile phone
2. The mobile phone adjusts the local phase reference
(1) Complete the phase synchronization between mobile phone and base station
3. The mobile phone dynamically measures the signal transmission delay between the mobile phone and the base station
(1) Base station dynamic measurement, the time difference TAd between the received signal of the mobile phone and the time slot of the local base station.
(2) TAd + TA0 is the current actual signal delay Td
4. Dynamic distance
Dynamic distance Sd = Td * V